Photochromic substances have been widely used in basic materials such as glass, plastic and the like to fabricate spectacle lenses, optical lenses, sunglasses, sun caps, ski goggles, toys, mirrors, glasses, films, building exterior materials, advertising materials, optical discs, etc.
Organic photochromic substances including a polymer matrix containing photochromic dyes are known through many theses and patents. In most of these substances, since the photochromic dyes are deteriorated and decomposed too fast by light, so that the average life span of the photochromic substance is not sufficient, there is a problem in that it is difficult to fabricate a product which is very useful for commercial purposes using the substances. As a result, there is a need for a stable organic photochromic substance.
In order to fabricate such a product, several methods have been proposed. For example, in order to endow a resultant polymer with a photochromic characteristic, there is a method in which the photochromic dye is incorporated into a polymerizable composition. However, there is also a problem that the photochromic dyes are sometimes damaged during a polymerizing process. To relieve the above problem, there are proposed some new solutions as described in U.S. Patent Application Nos. 60/000,829, 60/001,677 and 60/011,429.
In European Patent No. A0195898 and U.S. Pat. No. 4,720,356 corresponding to the European Patent, the photochromic dye is incorporated in a composition of polymerizable matrix of hindered amine as a light stabilizer called HALS (hindered amine light stabilizer). And, in Korean Patent Publication No. 2000-0067988, a matrix for photochromic compounds is disclosed in which a functionalized hindered amine light stabilizer capable of reacting with an isocyanate group is linked to the polymer backbone by a covalent bond to form a grafted structure, thereby having an effect on the photochromic dye, in particular, spirooxazines.
Meanwhile, Korean Patent Publication No. 1995-0009349 describes an encapsulated photochromic composition which is fabricated by using addition agent, oil and gelatin in a spyro-based photochromic substance in order to increase the stability of the photochromic substance. Further, Korean Patent Publication No. 2000-0024335 describes a method of prolonging the photochromic characteristic and heat stability by fabricating a core-shell type nano-capsule, as shown in FIG. 1, having a structure in which a diarylethene-based photochromic compound is surrounded by a high polymer.
Recently, in Korean Patent Publication No. 2004-0073217, there is disclosed an automotive windshield in which a photochromic solution is filled between two glass-substrates, and the color of which can be changed by ultraviolet rays, as shown in FIG. 2.
However, although the method of capsulating the photochromic substance provides an improved tolerance for the deterioration of the photochromic dye, there is also a problem in that it is difficult to commercialize the products due to the question of mass production and the increase in fabricating cost. Further, although the method of filling the photochromic substance between the two glass-substrates provides an extended life span of the product, when the ultraviolet rays are irradiated, the photochromic substance may be decomposed or deteriorated by permeating moisture or air from the outside; or by a very small amount of residual moisture, air, and impurities therein; and then since the decomposed radical substance further decomposes the adjacent photochromic substance, there is another problem in that the life span of the product is sharply reduced.